Centrifuges, such as screen scroll centrifuges, are often used to filter or dewater crystalline or amorphous solid/liquid slurries. These centrifuges typically utilize a screen to separate the solid portion of the slurry from the liquid phase. The screen, moreover, is typically sized to retain the larger solids portion of the slurry while allowing the liquid to pass through and thus the two phases of the slurry may be separately collected. Instead of relying on Earth's gravity to filter the slurry through the screen, however, filtration occurs under large centrifugal forces (on the order of many times the force of gravity), caused by high rotational speed of the centrifuge. These large centrifugal forces substantially increase the separation efficiency of the centrifuge.
Specifically, the slurry is delivered to the interior of a rotating basket that includes a conical screen portion. The conical screen portion is typically formed from a plurality of wire segments that are spaced side-by-side. For structural support, the wire segments may be welded to circumferential ribs spaced out along the axis of the basket. Rotation of the cone-shaped basket drives the slurry against the inner surface of the basket and the liquid phase is forced through the slots formed between adjacent wire segments. The larger solid particles do not pass through the slots and are instead collected on the inside of the basket.
To convey the solids out of the inside of the basket, a scroll conveyor having a helical blade is typically mounted concentrically within the basket. The tip of the blade, moreover, is spaced from the inner surface of the basket by a small radial clearance. The scroll conveyor is rotated in the same direction as the basket but at a slightly different rotational speed relative to the basket. Through this differential speed, the solids accumulating along the inside surface of the basket are conveyed by the helical blade from the small diameter end toward the basket's larger end where they are dumped in a discharge chute and collected.
Another type of separating centrifuge is a vibrating centrifuge. Vibrating centrifuges also include a screen basket that is similar in design to the basket of screen scroll centrifuges. A vibrating centrifuge, however, does not utilize a helically bladed scroll to move the solid particles collecting on the inside surface of the basket to the discharge chute. Instead, the vibrating centrifuge includes a mechanism for shaking the basket back-and-forth along its axis. By shaking or vibrating the basket along its axis, solid particles accumulating on the inside of the basket are conveyed axially toward the discharge chute and collected.
As shown, scroll and vibrating centrifuge are very useful for separating liquid/solid slurries. Nonetheless, these centrifuges are subject to significant wear requiring frequent maintenance and corresponding down time. For example, solid particles of the slurry often get trapped in the slots of the basket, damaging the screen and reducing the separation efficiency of the centrifuge. Furthermore, the slurries often include highly abrasive components that wear out the screen portion of the basket. The corresponding maintenance and replacement of parts significantly increase operating costs.
An improvement to the conventional screen basket is described in U.S. Pat. No. 5,378,364 commonly owned by the assignee of the present application. In the '364 patent, the conventional wedge wire basket is replaced with a wear resistant basket. In particular, the basket includes an outer structure having a plurality of closely spaced apertures or windows. Bridging each aperture or window are a plurality of wear resistant ligaments arranged to form screen sections. The ligaments may be formed from tungsten carbide which has improved wear characteristics as compared to the more conventional wedge wire. The tungsten carbide ligaments are typically spaced side-by-side inside the basket. The spaces between adjacent ligaments form slots through which the liquid portion of a slurry passes. The configuration and arrangement of the ligaments, moreover, reduce the chances of entrapment of solid particles in the slots.
Although the wear resistant basket of the '364 patent presents a significant improvement in scroll centrifuges, it is nevertheless costly to manufacture. Specifically, as set forth above, the screen elements of the wear resistant basket are typically formed from tungsten carbide ligaments and extend the full length of the basket. Since tungsten carbide is a relatively expensive material, the cost of manufacturing such baskets is high. In addition, the ligaments are typically installed within the basket by hand further increasing the manufacturing costs of such baskets. Thus, it is desirable to develop a screen basket having wear resistant features but at a lower cost.